An electrochemical measuring method which makes use of an electrochemical reaction in a solution has been often used in analyses in fields such as a biological field, an environmental field, a medical field, and a food field. For example, an immunoanalytical method utilizing an electrochemical detection is used for analyzing trace substances (such as protein and hormone) in a biologic sample. An electrochemical measurement electrode used in such an analysis is configured by providing, on a substrate, predetermined electrodes (such as a working electrode and a reference electrode) made of a conductive material. For example, Patent Literature 1 discloses a flat electrochemical measurement electrode in which a working electrode, a counter electrode, and a reference electrode are provided on an insulating substrate by patterning a conductive material.
Patent Literature 2 discloses an electrochemical measurement electrode in which an electrode made of a noble metal is provided on part of a printed section on a printed-wiring board and the rest of the printed section is insulated by an insulator.
According to the electrochemical measurement electrodes disclosed in Patent Literatures 1 and 2, an electrode made of silver and silver chloride is used as the reference electrode. Such an electrode made of silver and silver chloride is one of reference electrodes which have been widely used, because the electrode (i) has a simple structure and thereby is easy to handle and (ii) has good reproducibility of an electric potential.
Patent Literature 3 discloses a comparison electrode which includes an internal liquid in which an inner electrode made of silver and silver chloride is disposed. Such a comparison electrode is used in a pH measurement, etc. Specifically, a pH measurement of a target solution is carried out with the use of (i) the comparison electrode in which the internal liquid is sealed and (ii) another electrode which is disposed in the target solution and is separated from the internal liquid. According to the technique disclosed in Patent Literature 3, an inorganic cation-exchange agent, which captures a silver ion and/or a chloro complex ion, is provided in the comparison electrode for preventing deposition of the silver chloride in the internal liquid.